But most experts now recommend the chicken pox vaccine, and many schools and daycare centers require it. Here's why:

Chicken pox is no party. If your child gets it, he's likely to develop a rash of itchy, painful blisters accompanied by fever and fatigue. If the blisters get infected, he may need antibiotics. They may also leave permanent scars, possibly on his face. If he's going to daycare or school when he gets chicken pox, he'll have to stay home for eight or nine days.

Chicken pox can be serious and even deadly. Before the vaccine, chicken pox caused an average of 10,600 hospitalizations and 100 to 150 deaths a year in the United States. Most of the severe complications and deaths occurred in previously healthy people.

The vaccine protects children from the worst of this illness. While the vaccine isn't 100 percent effective (9 of every 10 people vaccinated are completely protected), vaccinated children who do come down with it will have only very mild symptoms. That usually means fewer than 50 blisters, no fever, and less sick time.

The vaccine may help protect your child against a related disease called shingles. About 1 out of 3 adults who have chicken pox earlier in life get this rash of extremely painful and disfiguring blisters.

Shingles appears when the chicken pox virus, which lives forever in the central nervous system, "reawakens" and becomes active again. People who were vaccinated against chicken pox may still get shingles, but will have a much less severe case than those who had the disease itself.

For all these reasons, both the American Academy of Pediatrics (AAP) and the Centers for Disease Control and Prevention (CDC) have put the chicken pox vaccine on the schedule of recommended immunizations.

What's the recommended schedule?

Recommended number of doses

Two shots at least three months apart.

Recommended ages

Between 12 and 15 months

Between 4 and 6 years

The chicken pox vaccine may be bundled with the vaccine for measles, mumps, and rubella in one shot, called the MMRV (measles-mumps-rubella-varicella).

Who shouldn't get the chicken pox vaccine?

A child who has ever had a severe allergic reaction to gelatin (yes, the stuff that's in Jell-O) or the antibiotic neomycin should not get the immunization. If a child has a severe allergic reaction to his first vaccination, he shouldn't receive a second.

If your child has cancer or any disease that affects his immune system, has recently had a blood transfusion, or is taking high doses of oral steroids (for asthma or poison ivy, for instance), his doctor will carefully evaluate whether giving him the vaccine is a good idea.

There's a higher risk of febrile seizures for some children with the MMRV vaccine. If your child has had a seizure or there's a family history of seizures, be sure he gets separate doses of the MMR and varicella vaccines.

Is the chicken pox vaccine a live vaccine?

Varicella is a live-attenuated vaccine. This means it's a live virus that's been weakened so that it's unlikely to cause the disease. Instead, the virus will replicate in the cells of the body and cause the body to produce an immune response, which should protect against a real chicken pox infection.

What are the possible side effects?

About 20 percent of children will have some soreness at the site of the injection. About 15 percent have a low-grade fever.

In rare cases, a child may get a very mild form of the disease. About 4 percent of children develop a mild rash (around ten chicken-pox-like blisters).

Fewer than 1 child in 2,500 has a seizure caused by high fever (and slightly more with the MMRV vaccine). Although febrile seizures may seem scary, they're almost always harmless for the child. Still, call your doctor right away if your child has one.

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